1. Field of the Invention
The present disclosure generally relates to human system reinforcement devices and methods. More particularly, the disclosure generally relates to plates (e.g., cervical) used to fuse and/or reinforce vertebrae including securing mechanisms configured to selectively restrict movement of fasteners used in combination with the plates.
2. Description of the Relevant Art
There exist systems and methods for fusion of the human cervical spine, and in particular plate systems for aligning and maintaining cervical vertebrae in a selected spatial relationship (e.g., during spinal fusion of those vertebrae).
Currently cervical plating systems are used for this purpose. Such systems are composed of one or more plates and fastening screws for aligning and holding vertebrae in a desired position relative to one another. The earliest devices consisted of stainless steel plates and screws and required that the screws pass entirely through the vertebrae and into the spinal canal in order to engage the posterior cortex of the vertebral bodies. This required the ability to observe or visualize this area, which can be problematic in, for example, the lower cervical spine where the vertebrae may be hidden by obstructions.
In order to form holes in the vertebrae for the insertion of screws, the vertebrae must be drilled and tapped. Each of these operations involved the passage of an instrument entirely through the associated vertebrae and into the spinal column. Thus, these instruments come into close proximity to the spinal cord and the dural sac which are in close proximity to the back surfaces of the vertebrae. Any procedure which introduces an object into the spinal canal presents serious risks which are of concern to the surgeon.
In current plating systems, problems exist with failure of the hardware (e.g., breakage of the screws and plates, and backing out of screws). These occurrences may require surgical procedures to replace the broken parts or the plates and screws entirely, and to repair any damage that may have been caused.
The use of the known plating systems may result in a loss of lordosis (i.e., the normal curve of the cervical spine when viewed from the side).
Historically there have been many ways to prevent screws from backing out during anterior cervical/lumbar plating. These mechanisms are vast including everything from screws locking directly into the plate to screw cover mechanisms that prevent back out. However, current technology does not allow for controlled settling of the spinal column (leading, for example, to an increased risk of non-fusion). A benefit of controlled settling is that it increases the chance a fusion occurs because bone healing requires a good balance between stability and loading. This is called shared loading. The fracture must be kept stable during the healing process but not totally off-loaded or else the fracture will not unite. A plate system optimally needs to inhibit lateral relative displacement of coupled vertebrae while at the same time allowing vertical relative displacement of the vertebrae which causes compressive loading on the intervening grafts which in turn leads to boney fusion.
Therefore a plating system and/or method which inhibits fastener back out while allowing movement of fasteners in substantially parallel to or in the sagittal plane would be highly desirable.